I arrived late in this thread, but here go my thoughts on this subject:
First, I have to say that I'm a bit surprised by the experiences shared here, both from expats and locals.
I am a local, and if I ever come across someone who says that he/she has only room for friends from the neighbourhood, elementary school and the like (eg those whose friendship started very early in life), I'd just considered it weird, and certainly not a representative Argentinian trait.
To tell you the truth, I came across people like that, but in rare occasions. All the people I know (including myself) are open to new friends and do have friends that they picked up in different stages of life.
I, for example, have friends from work and college (the present), some from high school (I really don't see them often), and I don't have friends from elementary school. Well, I have to admit that two years ago I participated in a reunion of my elementary school classmates (some of them), and since then, from time to time, we meet to have a nice time, but that was thanks to Facebook! And BTW, we can have like months on end without being in contact and it's ok.
I think, though, that there is some truth in the fact that Argentinians tend to keep earlier friendships more than in, say, US. But that is just that: a tendency, a question of degree. Not to be taken as representative of the whole Argentinians. And BTW, if someone tends to keep more friendships from the past, that doesn't necessarily mean that he/she is closed to any new friendship. But again, this is just a tendency.
My view is that some expats have encountered some people here that match this tendency: "In Argentina people tend to keep friendships from the past more than in other places". And, based on this, those expats generalize and think that it's representative of Argentinians to be like that.
It's as if I go to country X and see that there are more blond people than in my country, and then I think "People from country X are blond", whereas maybe a minority are blond in country X, but just a bigger minority than in my country.
Finally, I would like to say that I'm NOT trying to imply that some of the posters here ACTUALLY went along the lines of the reasoning mentioned above (the one exemplified by country X and blonds), but that's the impression I got when I read the threads, just that.
Cheers,
Santiago
.... Usually the opposite, mind you, I am originally from the emerald isle.... 
